[tex]\frac{a}{b}=\frac{3}{4}\Rightarrow a=\frac{3b}{4}\\
\frac{a-6}{b+4}=\frac{1}{2}\\
2(a-6)=b+4\\
2(\frac{3b}{4}-6)=b+4\\
\frac{3b}{2}-12=b+4\\
\frac{3b}{2}-b=16|\cdot 2\\
3b-2b=32\\
\boxed{\boxed{\boxed{b=32}}}\\
\\
a=\frac{3b}{4}\\
a=\frac{3\cdot 32}{4}\\
\boxed{\bxoed{\boxed{\boxed{a=24}}}}[/tex]